1. Field of the Invention
The present invention relates to an integrated process of using a chloric acid solution to separate mixtures of zinc oxide and manganese oxide by converting the manganese oxide into manganese dioxide and also recovering the zinc and chloric acid values.
2. Brief Description of the Art
The recycling of used batteries is a relatively simple process which starts with expended or defective batteries being milled and then passed through a magnetic separator to remove the iron battery jacket. The resulting iron-free mixture of compounds is heated to temperatures in excess of 300.degree. C. and washed to yield, among other things, a mixture of zinc and manganese oxides. This mixture is stable and non-polluting. This recycling process is advantageous because it results in the production of a stable non-toxic zinc and manganese oxide complex from potentially toxic battery waste. The disadvantage has been that it has not previously been possible to separate the mixture of oxides using existing processing methods. This has resulted in the waste of significant quantities of zinc and manganese metals.
The compounds that are the subject of this reaction are known in the art. Zinc oxide (ZnO) is a white solid that has a molecular weight of 81.38. It has a melting point of 1,975.degree. C. and is soluble in acid, alkali and ammonium chloride. Zinc oxide is insoluble in alcohol and ammonia. Because of its use in the vulcanization process the rubber industry is the largest user of zinc oxide. In addition to many other uses, zinc oxide has also been used as an ingredient in paints, as a trace element nutrient for agricultural products and as a photocopying aid.
Manganese oxide, Mn.sub.3 O.sub.4, (also known as manganic manganese oxide) has a molecular weight of 228.81 and is thermally the most stable manganese oxide. It is generally in the form of black rhombi crystals that have a melting point of 1,564.degree. C. Manganese oxide is soluble in hydrochloric acid but insoluble in hot and cold water. Different manganese oxides (e.g. Mn.sub.2 O.sub.3 --manganic oxide; MnO--manganous oxide) may be present as well as mixtures of different manganese oxides.
Chloric acid (HClO.sub.3) is a strong oxidizing agent whose oxidizing properties vary somewhat with the pH and temperature of the solution. It is fairly stable in cold water solutions of up to about 30% by weight. Upon heating, chlorine and chlorine dioxide may be evolved depending upon the strength of the solution. Aqueous chloric acid solutions may be concentrated by evaporation under reduced pressure to where the chloric acid concentration is greater than 40% by weight.
Manganese dioxide (MnO.sub.2) (also known as manganese binoxide, manganese peroxide; manganese superoxide; and black manganese) is a strong oxidizer and is used in the manufacture of manganese steel; in alkaline batteries (dry cells); for making amethyst glass or decolorizing glass; and painting on porcelain, faience, and majolica. It is also used in electrotechnics, pigments, browning gun barrels, drier for paints and varnishes, printing; dyeing textiles; and making potassium permanganate. It is characterized as follows: has a molecular weight of 86.94; when ignited, evolves oxygen and leaves Mn.sub.3 O.sub.4 ; insoluble in water, nitric acid, or cold sulfuric acid; slowly dissolves in cold HCl with evolution of Cl.sub.2 ; in the presence of hydrogen peroxide or oxalic acid, it dissolves in dilute H.sub.2 SO.sub.4 or HNO.sub.3.
Manganese dioxide is a naturally occurring substance; it occurs in nature as the mineral pyrolusite. It is also made artificially by various processes.
U.S. Pat. No. 3,640,683, which issued to Miyazaki et al. on Feb. 8, 1972, teaches several processes for making manganese dioxide:
(1) thermal decomposition of manganese nitrate (MnNO.sub.3) to manganese dioxide and NO gas;
(2) oxidation of manganese hydroxide [Mn(OH).sub.2 ] particles with air or an oxidizing agent or oxygen or ozone to form manganese dioxide;
(3) oxidation of manganese sulfate (MNSO.sub.4) with an oxidizing agent (e.g., chlorate, hypochlorite, permanganate, or peroxide) to form manganese dioxide and by-product salts and gases;
(4) disproportion of a manganese sub-oxide (Mn.sub.2 O.sub.3) with sulfuric acid to form manganese dioxide and a manganese sulfate by-product;
(5) thermal decomposition of manganese chloride; and
(6) roasting a naturally occurring, but crude, manganese dioxide-containing ore with air or oxygen; then reacting the roasted ore with a hot aqueous solution of chlorate salt and sulfuric acid; separating the formed needle-like manganese dioxide particles from the hot aqueous solution and then washing the separated manganese dioxide with water.
U.S. Pat. No. 4,402,931, which issued to Tanabe et al. on Sep. 6, 1983, teaches a process of producing manganese dioxide by (1) heating and decomposing a solution of ammonia complex of manganese (manganese ammonium carbamate) at a temperature of 68.degree.-80.degree. C.; (2) then optionally roasting the resulting manganese carbonate in air containing 15-85% steam; (3) roasting the manganese carbonate at a temperature of 275.degree.-375.degree. C. in oxygen containing 15-85% steam; and (4) treating the resulting manganese dioxide by heating it in either (a) a diluted sulfuric acid, (b) a solution of sulfuric acid and chlorate, or (c) a solution of sulfuric acid, manganese carbonate and chlorate.
In the commercial process for producing manganese dioxide by chemical oxidation that involves an acidic solution made by sulfuric acid and sodium chlorate salt, the oxidation reaction consumes chlorate and releases chlorine (Cl.sub.2) and chlorine dioxide (ClO.sub.2) gases as well as producing sodium ions, sulfate ions, sulfuric acid, and chlorate ions as by-products which must be purged from the system. The chlorine (Cl.sub.2) and chlorine dioxide (ClO.sub.2) gases may be hazardous if large concentrations are formed. These gases and the by-products require neutralization, which may involved large quantities of a base. Accordingly, such processes have important commercial limitations.
U.S. Pat. No. 5,279,743, which issued on Jan. 18, 1994, teaches a process of separating zinc and manganese oxide by (1) reacting said oxide mixture with a chloric acid solution to form a mixture having a solid phase containing manganese dioxide and a liquid phase containing chloric acid solution and dissolved zinc ions contained therein and (2) then separating the solid and liquid phases. This patent further teaches mixing the separated solid phase with a second chloric acid solution to dissolve remaining zinc oxide in the manganese dioxide and then separating that second chloric acid solution containing additional zinc ions from a substantially pure solid manganese dioxide product.
While the teachings of U.S. Pat. No. 5,279,743 represent a significant commercial advance over the preexisting oxidation routes for making manganese dioxide, the problem of recovering both the valuable zinc and chloric acid after separation of the solid manganese dioxide exists.
U.S. patent application Ser. No. 08/180,838, filed Jan. 12, 1994, is directed to reacting manganese oxide with a molar excess of an aqueous chloric acid solution, in a reaction zone to form a liquid/solid reaction mixture wherein the liquid phase contains chloric acid and water and the solid phase contains manganese dioxide; then separating the solid phase from the liquid phase; and removing water from the liquid phase to further concentrate said chloric acid; and finally returning said separated and concentrated chloric acid back to the reaction zone for further reaction with manganese oxide. While this process is an improvement over the process of U.S. Pat. No. 5,279,743 in that the chloric acid values are recovered and reused, it does not offer any answer toward recovering zinc values if zinc oxide is originally present with the manganese oxide. The present invention offers a solution to that remaining problem.